The value of the mouse as a model for the study of prostatic hyperplasia and neoplasia is being examined. Differences in prostatic structure between 24 inbred strains of mouse are in process of being analyzed, as a basis for determining which strains are more susceptible to pathological changes with age. One spontaneous adenocarcinoma has been found, and other tumors in the prostates of aged mice are being sought. Prostatic epithelium from strains in which a high proportion of the gland is epithelial is being grown in cell culture in defined media, without serum, but supplemented with hormones, high zinc, growth factors (e.g. epidermal growth factor) and other adjuvants (e.g. transferrin, spermine). Identification of the origin of the cells as acinar or stromal has been made on the basis of histochemical acid or alkaline phosphatase reactions. Confirmatory identification of the acid phosphatase localization will be made using a 125I radioimmunoassay. Further improvements in medium composition are being investigated. Long-term (greater than 200 days) cultures have been achieved, and conditions that lead to the establishment of cell lines are being explored.